We invited 15 ISPs that we understood to have built out national IP backbones. In addition to the seven vendors we tested, the invitation list included Ardent Communications, AT&T, Broadwing Communications, Epoch, Genuity, SBC Communications, Verizon and WorldCom.We invited 15 ISPs that we understood to have built out national IP backbones. In addition to the seven vendors we tested, the invitation list included\u00a0Ardent Communications,\u00a0AT&T,\u00a0Broadwing Communications,\u00a0Epoch,\u00a0Genuity,\u00a0SBC Communications,\u00a0Verizon\u00a0and\u00a0WorldCom.Both AT&T and WorldCom originally agreed to take part in the test, but bowed out during the ramp-up period, citing methodology issues.Ardent, Broadwing and SBC did not respond to our invitation despite multiple attempts to contact them. Epoch met with us once to discuss methodology but did not respond to further attempts to get the company to participate. Genuity and Verizon representatives declined to participate but expressed a willingness to participate in future tests.